This invention relates to a radio control device for remotely controlling a controlled unit or a radio control model mounted with a receiver such as, for example, a model airplane, a model vehicle, a model ship or the like by radio transmission from a transmitter, and more particularly to a radio control device for carrying out remote control of a radio control model by radio transmission, a transmitter constituting a transmission section of the radio control device, a high frequency module and a pulse generating unit each incorporated in the transmitter, and a receiver mounted on the radio control model and constituting a receiving section of the radio control device.
In general, in radio control device for carrying out remote control of a radio control model, an amplitude modulation system (hereinafter referred to as "AM system") and a frequency modulation system (hereinafter referred to as "FM system") are known as a modulation system for modulating a main carrier applied to remote control of the radio control model by radio transmission and receiving. Also, a pulse position modulation system (hereinafter referred to as "PPM system") and a pulse code modulation system (hereinafter referred to as "PCM system") are known as a signal modulation system for modulating the main carrier.
Each country defines by law a signal carrier for control by remote radio transmission and receiving. The law causes the radio control device to be subject to regulation on a usable frequency band. For example, Japan regulates that bands of 27 MHz and 40 MHz are usable frequency bands for remote control. Further, a predetermined number of frequencies are allowed in each of the usable frequency bands.
More particularly, in the case of the 27 MHz band, twelve band sections are defined at every 50 KHz interval in an area between 26.995 MHz and 27.245 MHz as shown in Table 1. In Table 1, A band section No. 12 commonly uses 27.245 MHz and 27.255 MHz.
TABLE 1 ______________________________________ 27 MHz Band Band Section No. Frequency (MHz) ______________________________________ 1 26.975 2 26.995 3 27.025 4 27.045 5 27.075 6 27.095 7 27.125 8 27.145 9 27.175 10 27.195 11 27.225 12 27.245 27.255 ______________________________________
Likewise, in the case of the 40 MHz band, thirteen band sections are defined at every 20 KHz interval in an area between 40.61 MHz and 40.85 MHz as shown in Table 2.
TABLE 2 ______________________________________ 40 MHz Band Band Section No. Frequency (MHz) ______________________________________ 61 40.61 63 40.63 65 40.65 67 40.67 69 40.69 71 40.71 73 40.73 75 40.75 77 40.77 79 40.79 81 40.81 83 40.83 85 40.85 ______________________________________
According to a law provided in the United States of America, a band of 72 MHz is divided into fifty band sections at every 20 KHz interval in an area between 72.01 MHz and 72.99 MHz. Germany provides a similar regulation on a usable frequency band.
In view of the above, the conventional radio control device is so constructed that a so-called high frequency module which is a circuit component formed by modularizing a high frequency circuit for determining a frequency band of a carrier and/or its kind can be readily incorporated in a rear side portion of a transmitter body. Thus, accommodation to a change in frequency band of a carrier is carried out by preparing a high frequency module depending on a frequency band allowed by each country and exchanging a crystal oscillator of a predetermined oscillating frequency called a crystal.
Also, in the conventional radio control device, much effort is directed to development of a frequency synthesizer system which utilizes a phase-locked loop (hereinafter referred to as "PLL circuit") circuit as the means for changing a frequency of a signal carrier.
The frequency synthesizer system utilizing the PLL circuit is adapted to set a variety of frequencies by changing a dividing ratio of an oscillating frequency. Unfortunately, use of the frequency synthesizer is restricted by the law of each of the countries.
For example, in Japan, self-imposed control regulations on a carrier frequency in a band of 40 MHz were established by "Standard of Certification and Qualification of Conformance to Recommended Standard of Transmitter for Radio Control (Notification No. 895 of the Ministry of Posts and Telecommunications dated Nov. 24, 1984)", so that a transmitter for a radio control device is required to meet the regulations. The regulations provide that "an oscillating system must be a crystal type transmission system", therefore, it is impossible to employ the frequency synthesizer system.
Likewise, in each of countries which lack provisions on such a transmission system, any frequency other than that allowed by the country cannot be used even if it allows the use of the frequency synthesizer system.
As will be noted from the above, the countries are different in laws such as regulations on a usable frequency band and a transmission system from each other. In view of such a difference, it would be considered that the transmitter is constructed so as to be accommodated to a frequency band allowed by each of the countries. However, this requires to prepare a number of transmitters depending on the countries, because applicability of the frequency synthesizer system is varied depending on the countries as described above. Also, even if a certain country allows use of the frequency synthesizer system, it is required to construct the transmitter so that a frequency other than that in a frequency band allowed by the country may not be used.
Further, in the transmitter for the radio control device, as described above, the system for modulating a main carrier for remotely controlling a radio control model includes the AM system and FM system. Also, the system for converting a signal for modulating the main carrier includes the PPM system and PCM system. In this instance, a pulse position modulating signal (hereinafter referred to as "PPM wave") used for the transmitter is processed by arranging one-shot pulse of a predetermined width (for example, 450 .mu.sec) in a serial manner and varying a position of each of the pulses, to thereby change a width of an output pulse of a transmission channel, resulting in an output of a receiver being controlled.
It is often desired that the radio control device concurrently carries out radio control of a plurality of controlled units in the same region. In this case, when frequencies for driving the controlled units are the same, there is a possibility that radio interference occurs between the controlled units, so that it is required to change the frequencies. Such a change in frequency is conventionally carried out by exchanging crystal oscillators so as to permit usable basis to differ from each other.
However, the change in frequency by exchange of the crystal oscillator causes an operator to always carry crystal oscillators different in frequency in order to avoid radio interference with another operator. In order to eliminate such a disadvantage, an effort is directed to development of a transmitter which is so constructed that the above-described PLL circuit which is generally used in the field of communications is incorporated therein to facilitate setting and changing of a required frequency without any exchange of circuit parts.
For example, a transmitter having such a PLL circuit incorporated therein which is manufactured according to the U.S. specifications is constructed in such a manner that when it is subject to modulation under the conditions that a time period in one frame T1, a one-shot pulse width T2, a channel pulse width T2 of each of channels near a neutral position and a central frequency F0 are set to be 22.5 msec, 450 .mu.sec, 1520 .mu.sec, 72.79 MHz and .+-.1.5 KHz, respectively, and a time constant of a low pass filter in the PLL circuit is sufficiently increased, a time period of F0+1.5 KHz and that of F0-1.5 KHz are repeated by 3600 .mu.sec and 18900 .mu.sec at every one frame, respectively.
In other words, when the PLL circuit is thus incorporated in the transmitter, lots of time is required for modulation on a negative side of the central frequency F0, so that a loop of the PLL circuit is operated to cause an output frequency of a voltage control oscillator to approach the central frequency F0 as much as possible, to thereby push up the central frequency F0 rather high.
This results in causing a deviation in the central frequency F0 which has been subject to PPM modulation. Also, the deviation is gradually increased with an increase in ratio of depth of the modulation with respect to the central frequency F0. Such an increase in central frequency F0 leads to a region overlapping an adjacent frequency corresponding thereto in another channel, to thereby cause a possibility of radio interference, resulting in a failure in remote control of the controlled unit with high accuracy.
Further, in the radio control unit of the frequency synthesizer system in which the PLL circuit is incorporated in the transmitter, changing-over of the frequency can be relatively readily carried out, for example, by changing over a dip switch to change a dividing ratio of a divider. However, the radio control device is constructed so that a receive frequency of the receiver is automatically changed over whenever the dividing ratio of the divider is changed due to changing-over of the switch during operation of the radio control device.
Therefore, changing-over of the switch due to any action on the controlled unit causes the dividing ratio to be automatically changed to lead to changing-over of the receive frequency, to thereby cause the receive frequency of the receiver to fail to coincide with a transmission frequency of the transmitter, resulting in failing in remote control of the controlled unit. The above-described action on the controlled unit includes, when the controlled unit is a model vehicle, vibration applied to a body of the vehicle due to unevenness of a road surface during traveling of the vehicle and vibration of an engine mounted on the body. Also, the action includes misoperation after the receive signal is set once.